JP3036207B2 - Method for producing silicon nitride sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a silicon nitride sintered body.

[0002]

2. Description of the Related Art A silicon nitride sintered body is produced by adding a sintering aid to silicon nitride powder, molding and sintering. Various oxides such as Y ₂ O ₃ , MgO, and Al ₂ O ₃ have been used as sintering aids and have been proposed. Albeit in a base material coated cutting tool, as a sintering aid to silicon nitride powder of 0.1 to 10 wt% Y ₂ O ₃ and 0.
Sintered body obtained by adding a 1 to 10 wt% of ZrO ₂ is disclosed in JP-A-61-101482, also the Y ₂ O ₃ as a sintering aid to a silicon nitride powder, further ZrO ₂ and SiO ₂ Has also been conventionally known.

[0003]

Conventionally, in a silicon nitride sintered body, normal pressure sintering was carried out at a temperature of 1500 ° C. to 170 ° C.
Room temperature to 1000 ° C by sintering at a relatively low temperature of 0 ° C
There is no report that the strength exceeded 1000 MPa (in air) in the range of, and more than 600 MPa at 1400 ° C in air. In order to obtain high strength, a dense and fine sintered body structure was required. For that purpose, it was necessary to sinter at a low temperature. Have been.

Accordingly, the present invention provides a silicon nitride sintered body which does not require HIP sintering, sinters under normal pressure, and sinters at a relatively low temperature of 1500 to 1700 ° C. and exhibits high strength at a high temperature. It is intended to provide a method of manufacturing.

[0005]

According to the present invention, a sintering aid is provided.
ZrO with various oxide auxiliary agents_TwoAnd SiO _Two
And zircon ZrO_Two・ Si
O_Two(ZrSiO_Four))
This solves the above problem. ZrO_TwoAnd SiO_Two
When added as single particles, it densifies, but
Drops.

Thus, according to the present invention, a uniform mixed powder obtained by adding at least ZrO ₂ · SiO ₂ and other oxide-based auxiliaries as a sintering auxiliary to a silicon nitride powder is formed, and the formed body is heated to 1500 ° C. A method for producing a silicon nitride sintered body, characterized by sintering at a temperature of １1700 ° C.
Silicon nitride powder as a starting material has an average particle size of 0.1 to
It is good to use the thing of 0.6 μm, more preferably 0.2-0.4 μm. This is because the driving force at the time of sintering is increased due to the small particle diameter of the starting material, and the particle diameter of the sintered particle is increased when the particle diameter of the starting material is increased, which causes a reduction in strength. Further, the purity is preferably 100 ppm or less of the total amount of metal impurities. This is because if the amount of impurities is more than this, the softening temperature of the grain boundary glass phase decreases, and the strength at high temperatures decreases.

The present invention is characterized in that zircon (ZrO ₂ .SiO ₂ ) is added together with the various oxide-based auxiliaries. Densified at a low temperature of 1500 to 1700 ° C. with silicon nitride powder raw materials and various oxide-based auxiliaries,
Further, even higher strength can be realized by adding zircon. As an oxide-based auxiliary agent other than zircon, typically, Y ₂ O
_{3, Yb 2 O 3, Al} 2 O 3, MgAl 2 O 4, TiO
₂ , ZrO ₂ , 3Al ₂ O ₃ .2SiO ₂ (mullite), and other rare earth metal oxides.
These auxiliaries generate a liquid phase with silicon oxide present on the surface of the silicon nitride powder particles, and are indispensable as liquid phase sintering accelerators in order to form a sufficiently dense sintered body at 1500 to 1700 ° C.

[0008] Examples of preferred oxide-based auxiliaries are Y_TwoO_Three, Y
_TwoO_Three+ MgAl_TwoO_Four, 3Al_TwoO_Three・ 2SiO
_Two(Mullite), Al_TwoO_ThreeAnd so on. Y_TwoO_ThreeAnd Y
_TwoO_Three+ MgAl_TwoO_FourIs 1000 ° C 4-point bending strength 10
Gives strength of more than 00MPa, mullite 1300-14
Gives high strength at 00 ° C. Y_TwoO_ThreeIs the needle-like β-S
i _ThreeN_FourPromotes crystal formation and reduces the aspect ratio of crystal grains
When it is increased, the strength and fracture toughness of the sintered body are improved. MgA
l_TwoO_FourHas the effect of lowering the sintering temperature,
As a result, a fine structure is expressed in the sintered body.

In the present invention, a sintering aid other than oxides may be additionally added. For example, AlN, Y ₂ (C
N ₂ ) ₃ and the like. The sintering aid has an average particle size of 0.05 to
0.5 μm, more preferably 0.3 μm, purity 99.0
% Or more is better. If the particle size is too large, the sinterability is reduced, and if there are many impurities, the desired strength cannot be obtained.

Although the amount of the sintering aid depends on the kind of the sintering aid, it is generally about 5 to 15% by weight, more preferably about 6 to 10% by weight based on the total amount of zircon and other oxide-based auxiliaries. Added. If it is less than 5% by weight, it will not be densified by normal pressure sintering, and the strength will not be obtained. Further, the ratio of zircon to other oxide-based auxiliaries is preferably 1/4 to 2/3 by weight ratio, but is preferably 1 to 3 in the case of zircon and mullite. If the ratio of zircon is smaller than these ratios, the effect of improving the high-temperature strength is reduced, and if the ratio is larger, densification is hindered.

Further, together with the sintering aid, amorphous Si
The addition of -NC powder produces fine SiC particles during the sintering process at the grain boundary triple point and in the grains, thereby forming 14 SiC particles.
At 00 ° C., the softening of the grain boundary phase is prevented, and the SiC particles are dispersed to provide resistance to crack growth, and the strength (particularly 1400 ° C.)
Strength) and the effect of improving fracture toughness. This amorphous S
i-N-C powder has a sintering temperature of about 30% by weight of SiC.
And 70% by weight of Si ₃ N ₄ , and a powder having an average particle diameter of 0.3 μm or less is preferable. Note that SiC powder may be directly added as powder having a similar particle size.

When the above-mentioned amorphous Si-NC powder is added, the content is preferably 3 to 20% by weight, more preferably 5 to 15% by weight.
The effect of addition becomes remarkable. The molding of the starting material powder can be performed by a conventional method. That is, typically, the starting powders are uniformly mixed and molded by isostatic pressing at a pressure of about 1000 to 3000 kg / cm ² .

Next, firing is performed.
Baking is performed in a temperature range of 500 to 1700 ° C. 1700 ° C
If the temperature exceeds the limit, thermal decomposition of zircon becomes remarkable, and the structure is not refined due to grain growth, so that the strength is reduced. On the other hand, if it is lower than 1500 ° C., a sufficiently dense sintered body cannot be obtained, and the strength is low. The firing atmosphere only needs to be inert,
For example, nitrogen such as nitrogen, argon, helium, or a mixed gas thereof is typically nitrogen.

The method for producing a silicon nitride sintered body of the present invention comprises:
Other than the above, it is possible to follow a common law. Further, in the present invention, there is an advantage that a sintered body having high strength can be obtained by normal-pressure low-temperature sintering, but pressure sintering has an effect of further improving strength.

[0015]

The sintering temperature is adjusted to 1500 to 1 by adding a sintering aid.
When the temperature is set to 700 ° C., the sintered structure is refined, and zircon is added, the strength at high temperatures is improved. Although the detailed action of zircon is unknown, it is thought that it increases the viscosity of the grain boundary phase at high temperatures and is effective in preventing softening.

[0016]

Example 1 Example 1 Si ₃ N ₄ powder (average particle size 0.5 μm or less, pregelatinization rate 92
97%) in the Y ₂ O ₃ powder (average particle size 0.3μm as a sintering aid, 99.9% purity), ZrO ₂ · SiO ₂ powder (mean particle size 0.5μm or less, more than 97% pure) Was mixed (silicon nitride ball mill) and 200
The molded body was press-molded at a pressure of kg / cm ² , the molded body was packed in thin rubber, vacuum-sealed, and then pressurized at a pressure of 3000 kg / cm ^{2 by} CIP. It was sintered in a furnace in _two atmospheres. The heating rate was 1 ° C./min, and the holding time at the highest temperature was 4 hours.

The four-point bending strength of these sintered bodies at room temperature (JI
SR 1601), high-temperature four-point bending strength (JIS A)
1604, in the atmosphere) and the average intensity is shown in Table 1. The relative density of the sintered body is a value obtained by dividing the bulk density obtained by the n-butanol substitution method by the theoretical density. For comparison, after being molded in the same manner as in Example 1, this molded body was sintered in a furnace in an N ₂ atmosphere under the conditions shown in Table 2 to obtain the results shown in Table 2.

[0018]

[Table 1]

[0019]

[Table 2]

Example 2 Si ₃ N ₄ powder (average particle size: 0.3 mm) produced by a thermal decomposition method of silicon diimide or a direct nitridation method of metallic silicon.
5 μm or less, α conversion 92-97%)
₂ O ₃ powder (average particle size 0.3 μm, purity 99.9%),
MgAl ₂ O ₄ powder (average particle size 0.3 μm or less, purity 9
9.9%), ZrO ₂ · SiO ₂ powder (average particle size 0.5
(a ball mill made of silicon nitride), press-molded under a pressure of 200 kg / cm ² , packed the molded product in a thin rubber, vacuum-sealed,
After pressurizing with IP at a pressure of 3000 kg / cm ² , this molded body was sintered in a furnace in an N ₂ atmosphere under the conditions shown in Table 3.
During the densification process, the temperature was raised at a rate of 1 ° C./min, and the holding time at the maximum temperature was 4 hours.

The four-point bending strength of these sintered bodies at room temperature (JI
SR 1601), high-temperature four-point bending strength (JIS R
1604, in the atmosphere) and the average intensity is shown in Table 3. The relative density of the sintered body is a value obtained by dividing the bulk density obtained by the n-butanol substitution method by the theoretical density. After being molded in the same manner as in Example 2, the molded body was sintered in a furnace in an N ₂ atmosphere under the conditions shown in Table 4 to obtain the results shown in Table 4.

[0022]

[Table 3]

[0023]

[Table 4]

As can be seen from Tables 3 and 4, Y ₂ O ₃ ,
By adding ZrO ₂ and SiO ₂ together with MgAl ₂ O ₄ as ZrSiO ₄ instead of alone and sintering at a low temperature of 1700 ° C. or less, a four-point bending strength value exceeding 1000 MPa even at 1000 ° C. and in air. Express
When the atmospheric pressure during sintering was increased, higher strength values were obtained (Sample Nos. 29, 30, 31).

It seems that the total amount of the sintering aid is preferably in the range of 5 to 15% by weight. If it is less than 5%, dense sintering will not be performed, and if it is more than 15%, the strength will decrease. When ZrO ₂ and SiO ₂ powders were separately added, Comparative Example No. As shown in FIG. 34, a dense sintered body is obtained, but the strength is reduced.

Also, Y ₂ O ₃ —MgAl ₂ O ₄ —ZrO
_{2, Y 2 O 3 -MgAl 2} O 4 -SiO 2, and Y ₂ O
₃ -MgAl Comparative Sample No. In ₂ O ₄ composition 35-3
As shown in FIG. 7, a dense sintered body can be obtained,
Significant decrease in strength at ℃. Example 3 Si ₃ N ₄ powder: Si produced by thermal decomposition of silicon diimide
₃ N ₄ powder (average particle size 0.2 μm, total amount of impurities 50 ppm
, Alpha conversion rate 97-100%) Si ₃ produced by direct nitriding of metallic silicon
N ₄ powder (average particle size 0.9 μm, total amount of impurities 980 ppm
Zircon (ZrSiO ₂ ) powder: average particle size 0.2 μm,
Purity 99% Other sintering aids: assistants in Tables 5 and 6, both having an average particle size of 0.2 to 0.6 μm and a purity of 99 to 99.9%.

The above powder was mixed with the composition (Si ₃ N
_{(4) The} powder was weighed in the balance of the sintering aid in a total of 100% by weight) and mixed with a silicon nitride ball mill in which impurities (inclusions) were minimized. 150 kg / cm of the obtained powder
Molding was performed at a pressure of ² and then packed in a thin rubber bag. After sealing in vacuum, hydrostatic pressure was applied at a pressure of 3000 kg / cm ² to complete the molding.

The compact was sintered in a nitrogen atmosphere at 1 atm under the conditions shown in Table 5. 1 ℃ over 1300 ℃
/ Min. The holding time at the sintering temperature was 4 hours. The obtained sintered body was machined and subjected to JIS-R-1
According to 601 and JIS-R-1604 standards, room-temperature and high-temperature four-point bending strengths were measured. Test number is 15-20
Here, the intensity values in Table 5 are arithmetic mean values.

The bulk density of the sintered body was measured by a substitution method using n-butanol, and all were 1.5% or less in total porosity. No pores of 1 μm or more were observed by optical microscope observation of the polished boundary surface. A molded body was molded and sintered in the same manner as in Example 3, but under the conditions shown in Table 6, and the results shown in Table 6 were obtained.

[0030]

[Table 5]

[0031]

[Table 6]

From Tables 5 and 6, Y ₂ O ₃ or Y ₂ O
It is recognized that the high-temperature strength can be improved not only in the combination of ₃ + MgAlO ₄ and zircon but also in the combination of various oxide-based auxiliaries and zircon. Example 4 Si ₃ N ₄ powder (average particle size: 0.3 μm, purity: 99.
99%), ZrSiO ₄ powder (average particle size: 0.3 μm, purity: 97% or more) as a sintering aid, and 3Al ₂ O
₃ · 2SiO ₂ powder (average particle size: 0.3 [mu] m, Purity: 9
8% or more) at the compounding ratio shown in Table 7, and Si ₃ N ₄
The mixture was uniformly mixed in ethanol with a ball mill manufactured by Co., Ltd., and then dried to obtain a mixed powder.

The above mixed powder is molded under pressure at a pressure of 150 kgf / cm ² , the molded body is packed in thin rubber, and after vacuum sealing,
CIP (Cold Isostatic Press)
By pressing at a pressure of 3000 kgf / cm ^{2 in} the treatment, a molded article having a predetermined shape (6 mm × 5 mm × 45 mm) was obtained. The compact was sintered in a furnace in a nitrogen atmosphere at the maximum heating temperature shown in Table 7 for 4 hours to obtain a sintered body. The heating rate at this time was 2 ° C./min.

Regarding these sintered bodies, JIS R 1
Room temperature, 1300 ° C, 1400 ° C in air according to 604
At each temperature, 20 four-point bending strengths were measured for each, and the average strength was determined. Table 7 shows the results.

[0035]

[Table 7]

As is clear from the results shown in Table 7, all of the sintered bodies according to the present example have high high-temperature strength at 1300 ° C. of 800 MPa or more, and high-temperature strength at 1400 ° C. of 700 MPa or more. Was. Further, in this example, the effect of sufficiently improving the strength was obtained even at normal pressure sintering. Sample No. sintered under pressure. In the sintered body according to No. 54, the strength was further improved.

It should be noted that the sintered body containing too much mullite had a low strength at a high temperature, and the sintered body containing too little mullite had a low strength. In addition, a sintered body in which the total amount of the sintering aid is too large has a high strength at room temperature, but has a high strength
And the high-temperature strength at 1400 ° C. decreased. Zircon 2
Additions in the range of 6% by weight and 2-4% by weight of mullite gave favorable results.

Example 5 The amorphous Si-NC powder used was subjected to a CVD reaction of, for example, hexamethyldisilazane and ammonia at 1000 ° C.
It is a composite powder produced by pyrolysis at 1350 ° C. in a N ₂ gas stream, and pyrolyzes to Si ₃ N ₄ and SiC at about 1500 ° C.

A Si ₃ N ₄ powder having an average particle size of 0.2 μm and a total amount of metal element impurities of 50 ppm was added to Y having an average particle size of 0.2 μm.
₂ O ₃ powder, ZrSiO ₄ powder, and amorphous Si—NC powder having an average particle diameter of 0.1 μm (composite powder of 30 wt% in terms of SiC generated by heating) were obtained to have the composition shown in Table 8. After weighing and uniformly mixing in ethanol, the mixed powder was molded into a mold, and then a hydrostatic pressure of 3 t / cm ² was applied to the molded body, and the molded body was sintered at a temperature of 1500 to 1700 ° C. After reaching the maximum temperature, the pressure was increased to a nitrogen gas pressure shown in Table 8 at a rate of 20 atm / min. The strength of the obtained sintered body was measured at room temperature and at a high temperature four-point bending test (J
IS-R-1601, 1604) and the results are shown in Table 8.

[0040]

[Table 8]

Comparing the results in Table 8 with those in Table 1, it can be seen that the high-temperature strength is further improved when amorphous Si-NC powder is further added together with the oxide auxiliary and zircon. This is because SiC is generated and dispersed in the grain boundaries and in the grains of the sintered body, so that it has the effect of preventing the softening of the grain boundary phase at high temperatures and stopping the progress of cracks, and has the effect of strength and fracture toughness. Is considered to be improved.

According to the results of experiments conducted on the same system as described above, the total amount of the oxide-based auxiliary agent and zircon was 3 to 10% by weight, and 2 to 15% by weight of the amorphous Si—N—C powder. When the amount of addition is within the range, the high temperature strength is remarkably improved, which is preferable.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-193666 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C04B 35/58

Claims (1)

(57) [Claims] At least ZrO ₂ · SiO ₂ (zircon) as a sintering aid and ZrO ₂ ·
A method for producing a silicon nitride sintered body, comprising forming a homogeneous mixed powder to which an oxide-based auxiliary agent other than SiO ₂ is added, and sintering the formed body at a temperature of 1500 to 1700 ° C.